The present invention relates to the art of corrosion-resistant metal materials such as a corrosion-resistant metal made of a corrosion-resistant metal alloy or a base metal which is coated with a corrosion resistant metal alloy, which corrosion-resistant metal materials can be used in a wide variety of applications such as, but not limited to, architectural or building materials such as roofing materials, siding materials, window frames, sheet metal, metal plates and the like; truck and automotive products such as, but not limited to, gasoline tanks, filter casings, body molding, body parts and the like; household products such as, but not limited to, appliance housings, electrical housings, light fixtures and the like; marine products such as, but not limited to, boat hulls, boat masts, dock system components; and/or other types of metal materials such as, but not limited to, tools, machinery, wires, cables, electrodes, solder and the like. The invention also relates to various metal alloy compositions or metal coating alloy compositions based upon metal alloys of tin and metal alloys of tin and zinc, and several novel methods and processes used therein for forming the metal alloy compositions or base metals coated with the metal alloy materials, such as but not limited to, wire or solder forming, metal strip forming, and coated metal forming by a plating process and/or a hot-dip process (i.e plating of metal alloy and subsequent flow heating, immersion in molten metal alloy, metal spraying of metal alloy, and/or roller coating of metal alloy), pretreatment of the base metal prior to metal alloy coating, applying an intermediate barrier metal layer prior to metal alloy coating, post-treating the metal alloy or coated base metal, and/or forming the metal alloy or coated base metal into a variety of different articles.
Over the last several years, there has been a trend in the industry to produce products which are higher in quality, are environmentally friendly, and are safe for use by humans, animals, and/or plants. This push for quality, safety and environmental friendliness is very apparent in the automotive industry wherein both consumer groups and environmental organizations are constantly lobbying for safer, higher-quality vehicles that are more fuel efficient and less detrimental to the environment. Recycling old vehicles has been one answer to resolving the environmental issues associated with vehicles which have run out their useful life. Automotive salvage markets have developed for these vehicles. The vehicles are partially dismantled and sold as scrap metal wherein the metal is melted down and reformed into various parts. Because of the environmentally-un-friendly nature of lead, the gasoline tanks of vehicles must be removed prior to the recycling of the vehicle. Gasoline tanks are commonly made of carbon or stainless steel that are coated with a terne alloy.
Terne or terne alloy is a term commonly used to describe a metal alloy containing about 80% lead and the balance tin. The terne alloy is conventionally applied to a base metal by immersing the base metal into a molten bath of terne metal by a continuous or batch process.
Although terne coated metals have excellent corrosion-resistant properties and have been used in various applications, terne coated materials have been questioned due to environmental concerns based on the high lead content of the alloy. Environmental and public safety laws have been proposed and/or passed prohibiting or penalizing the user of materials containing a significant portion of lead. As a result, these terne coated gas tanks must be disposed of in dumping yards or landfills. Not only does the terne coated gasoline tank take up space in the landfills, but there is a concern with the lead leaching from the terne coating into the landfill site and potentially contaminating the surrounding area and underground water reservoirs. Plastic gasoline tanks have been used as an alternative to terne coated materials, but with limited success. Although the use of plastic tanks eliminates the environmental concerns associated with lead, the plastic in-of-itself is a non-environmentally-friendly compound which does not readily degrade and therefore must be disposed of in a landfill. The plastic used to make the gasoline tanks is usually not the type that can be recycled. Plastics have also been found to be less reliable than metal gasoline tanks with respect to durability and safety. Plastic gasoline tanks have a tendency to rupture upon impact, such as from a car accident, whereas a metal gasoline tank tends to absorb much of the shock on impact by bending and slightly deforming. Furthermore, the plastic gasoline tanks are more susceptible to being punctured from roadside debris since the plastic skin is not as strong or malleable as the skin of a metal gasoline tank. Plastic gasoline tanks also require new materials, special tools and new assembly methods to fix and install the gasoline tanks due to the nature of plastic and its physical properties. These additional costs and shortcomings of plastic tanks have resulted in very little adoption of plastic gasoline tanks in present day motor vehicles.
The lead content in metal materials is also of some concern for building materials. This is especially a concern when the metal materials are in contact with drinking water. In many countries lead pipe has been outlawed to reduce the amount of lead in the water. In many remote locations throughout the world, piped water or well water is not readily available. As a result, structures, such as portable roof systems, are built to capture rain and to store the rain water for later use. These potable roof systems supply an important water source for inhabitants utilizing such structures. Roof systems that are designed to collect rain water are typically made of metal to increase the longevity of the roofing system. Typically, the roof systems are made of carbon steel since such metal is the least expensive. The carbon steel is commonly coated with a terne alloy to extend the life of the roof system. Terne alloy is commonly used due to its relatively low cost, ease of application, excellent corrosion-resistant properties and desirable colorization during weathering. Roof systems have been made of other metals such as, but not limited to, stainless steel, copper, copper alloys and aluminum. Stainless steel, copper, copper alloys and aluminum were typically not coated with a terne coating since these metals have excellent corrosion-resistant properties. However, in some limited applications, these metals have been coated with terne to extend the life of these metals. However, as with lead piping, there is a concern that the lead in the terne coated roofing materials results in lead dissolving in the collected water.
Terne coated materials have typically been coated with a 6-8 lb. coating (7-11 microns), which is a very thin coating. This thin coating commonly includes pinholes. Terne coated materials that are drawn or formed in various types of materials such as, but not limited to, gasoline tanks, corrugated roofing materials and the like typically included one or more defects in the coating. The defects in the terne coating on the base metal which were designed to protect the base metal from corroding thus compromised the corrosion resistance provided by the terne coating. Due to the thin layer of the terne coating and the pinholes in the coating, the coating on the base metal, upon being drawn by a die or by being formed, tended to tear or shear the terne coating and/or elongate the pin holes on the coating thereby exposing the base metal. These exposed surfaces were subject to corrosion and over time compromised the structural integrity, safety and/or performance of the coated base metal. The non-uniform coating of stainless steel metal with the terne coating is especially evident since the terne alloy did not bond as well to the stainless steel. Another disadvantage of using a terne alloy coating is the softness of the terne layer. The softness of the terne coating is susceptible to damage from the abrasive nature of forming machines and to environments that subject the terne coating to frequent contact with other materials.
Terne alloys have a further disadvantage in that the newly applied terne is very shiny and highly reflective. As a result, the highly reflective coating cannot immediately be used in certain environments such as on buildings or roofing systems in or near airports and military establishments. The terne coating eventually loses its highly reflective properties as the components of the terne coating are reduced (weathered); however, the desired amount of reduction takes at least approximately 1-½ to 2 years when the terne coating is exposed to the atmosphere, thus requiring the terne metals to be stored over long periods of time prior to being used in these special areas. The storage time is significantly prolonged when the terne coated materials are stored in rolls and/or the terne alloy is protected from the atmosphere.
Metallic coatings such as tin or zinc have been tested as substitutes for terne coatings with limited success. The most popular process for applying a tin coating to a base metal is by an electroplating process. In an electroplating process, the coating thickness is very thin and typically ranges between 0.3 microns to 30 microns. The very thin thicknesses of the tin coating typically results in a tin coating having a network of small pinholes, thereby making the coated material generally unacceptable for use in corrosive environments such as on building materials and automotive products. Such tin plated base metals can include a flash or intermediate metal layer (plated layer) to reduce the pinhole problems inherent with the tin plating process. The tin plated layer is also susceptible to flaking or being scrapped off when the tin plated base metal is drawn through a die and/or formed into various components. The flaking of the tin coating can also cause premature clogging of filter systems and liquid lines, such as in gasoline lines and filters, when the tin plated based metals are formed into gasoline tanks. The pinholes problem and flaking and/or scraping problem that is associated with plated tin coatings is very problematic since tin is not electroprotective under oxidizing conditions. Consequently, discontinuities in the plated tin coating result in the corrosion of the exposed base metal.
The plated tin coating of carbon steel is a well-known process in the food industry. However, in the specialized art of building materials, a tin coating for base metals for use on building materials and the like has recently been used as disclosed in U.S. Pat. No. 5,314,758. Tin coatings form a highly-reflective surface. As a result, materials coated with a tin coating cannot be used in an environment where highly-reflective materials are undesirable until the tin coated materials are further treated (i.e. paint) or the tin is allowed time to sufficiently oxidize.
Coating a base metal with zinc metal, commonly known as galvanizing, is another popular metal treatment to inhibit corrosion. Zinc is a desirable metal to coat materials because of its relatively low cost, ease of application, and excellent corrosion resistance. Zinc is also electroprotective under oxidizing conditions and inhibits or prevents the exposed metal, due to discontinuities in the zinc coating, from rapidly corroding. This electrolytic protection extends away from the zinc coating over exposed metal surfaces for a sufficient distance to protect the exposed metal at cut edges, scratches, and other coating discontinuities. Although zinc coatings bond to many types of metals, the bond is typically not very strong thereby resulting in the zinc coating flaking off the base metal over time and/or when being formed. The flaking of zinc, like the flaking of tin, can cause premature clogging of filter systems and liquid lines when zinc coated materials are formed into gasoline tanks. Further, when using fuel injection systems, the small particles of zinc or zinc oxide can disable the fuel injectors over time. Such problems are unacceptable in the automotive field. Zinc further does not form a uniform and/or thick coating when coating stainless steel, thus resulting in discontinuities in the coating. Zinc is also a very rigid and brittle metal, thus tends to crack and/or flake off when the zinc coated materials are formed and/or drawn through a die. When zinc oxidizes, the zinc coating forms a white powdery texture (zinc oxide). This white powdery substance is undesirable for many building applications and in various other environments and applications. Consequently, the use of a tin or zinc coating as a substitute for terne coatings has not been highly reliable, or a cost effective substitute for traditional terne coatings.
Metal coatings that include a hot dip coating of tin and zinc alloy have been used for fuel tanks as disclosed in Japanese Patent Application No. 47-97776 filed Sep. 29, 1972. The alloy coating thickness was disclosed to be 10-15 microns.
Metal coatings that include tin and zinc have also been used to coated base metals. Electroplating a tin and zinc mixture onto a steel sheet is disclosed in Japanese Patent Application No. 56-144738 filed Sep. 16, 1981. The Japanese patent application discloses the plating of a steel sheet with a tin and zinc mixture to form a coating thickness of less than 20 microns. The Japanese patent application discloses that after plating, pin holes exist in the coating and subject the coating to corrosion. The pin holes are a result of the crystalline layer of the tin and zinc mixture slowly forming during the plating process. Consequently, the Japanese patent application discloses that the plated tin and zinc coating must be covered with chromate or phosphoric acid to fill the pin holes to prevent corrosion. The Japanese patent application discloses that a preplated layer of nickel, tin or cobalt on the steel sheet surface is needed so that the plated tin and zinc mixture will adhere to the steel sheet.
The coating of steel articles by a batch hot-dip process with a tin, zinc and aluminum mixture is disclosed in U.S. Pat. No. 3,962,501 issued Jun. 8, 1976. The '501 patent discloses that the tin, zinc and aluminum mixture resists oxidation and maintains a metallic luster.
The '501 patent also discloses that the coating is applied by a batch process involving the immersion of a steel article into a molten alloy bath for an extended period of time. The '501 patent further also discloses that a molten tin and zinc metal alloy is very susceptible to oxidation resulting in viscous oxides forming on the surface of the molten tin and zinc metal alloy. These viscous oxides cause severe problems with the coating process. While the steel article is immersed in the molten alloy, a large amount of dross forms on the surface of the molten alloy. The dross results in non-uniformity of the coating and the formation of pin holes as the steel article is removed from the molten metal.
The '501 patent also discloses that the addition of up to 25% aluminum to the tin and zinc metal alloy inhibits dross formation, prevents Zn—Fe alloy formation, and reduces viscous oxide formation on the molten bath surface. The batch process disclosed in the '501 patent subjects the surface of the article to differing residence times in the molten alloy which can result in differing coating thicknesses and coating properties on the coated article.
The treatment of a steel sheet by plating tin and zinc followed by heat flowing is disclosed in U.S. Pat. No. 4,999,258. The '258 patent discloses a steel sheet plated with a layer of tin and a subsequent layer of zinc. The tin and zinc plated layers are then heated until the zinc alloys with the tin. The tin is applied at 0.2-1.0 g/m2 and the zinc is applied at 0.01-0.3 g/m2. The '258 patent also discloses that when less than 1% zinc is used, the beneficial effect of the zinc is null; however, when more than 30% zinc is used, the coating will rapidly corrode under adverse environments. The '258 patent also discloses that a nickel plated layer is preferably applied to the steel sheet prior to applying the tin and zinc plated layers to improve corrosion resistance. The heat treated tin and zinc layer can be further treated by applying a chromate treatment to the plated layer further to improve corrosion resistance.
A continuous process for electroplating a carbon steel strip is disclosed in U.S. Pat. No. 5,203,985. The '985 patent discloses that nickel is electroplated on a continuously moving strip of carbon steel. After the carbon steel has been nickel plated, the plated strip is hot dip coated with molten zinc.
The electroplating of tin, tin-nickel or tin and zinc by an electroplating process and subsequent formation of an intermetallic layer by heat flowing the plated layer is disclosed in U.S. Pat. No. 5,433,839.
Due to the various environmental concerns and problems associated with corrosion-resistant coatings applied to base metals and the problems associated with the inadvertent removal of the corrosion-resistant coating during the forming and/or drawing of the coated materials, there has been a demand for a coating or metal material that is corrosion-resistant, is environmentally friendly, and resists damage during forming into end components. Many of these demands where met by the tin metal alloy or the tin and zinc metal alloy and process and method for applying these alloys to a base metal disclosed in Applicants' U.S. Pat. Nos. 5,314,758; 5,354,624; 5,395,702; 5,395,703; 5,397,652; 5,401,586; 5,429,882; 5,455,122; 5,470,667; 5,480,731; 5,489,490; 5,491,035; 5,491,036; 5,492,772; 5,520,964; 5,597,656; 5,616,424; and 5,667,849. The present invention is an improvement or refinement of the alloys and/or use of the alloys disclosed in these prior patents.